1. Field of the Invention
The present invention relates to a fuel container having high gasoline barrier properties.
2. Description of the Related Art
In recent years, coextrusion blow-molded containers made of plastic materials are preferably used for containers for storing fuels, such as gasoline, and examples for such containers are the fuel tanks of motor vehicles. As for the plastic material used as the material of such containers, there are high expectations in polyethylene (especially very high-density polyethylene) with regard to economic efficiency, molding processability, mechanical strength, and the like. However, it is known that fuel tanks made of polyethylene have a disadvantage that the stored liquid gasoline and/or the vaporized gasoline easily permeates through the polyethylene walls into the atmosphere.
To eliminate this disadvantage, a method is known in which a halogen gas (e.g. fluorine, chlorine, or bromine) or sulfur trioxide (SO3) or the like is blown into the polyethylene container, and the inner wall of the container is halogenized or sulfonated. Another method that is known is to obtain a container that has a multilayered structure and is made of a polyamide resin layer and a polyethylene resin layer (see Japanese Laid-Open Patent Publication No.6-134947, U.S. Pat. No. 5,441,781). Yet another method that is known is to obtain a container that has a multilayered structure and is made of an ethylene-vinyl alcohol copolymer (EVOH) resin layer and a polyethylene resin layer (see U.S. Pat. No. 5,849,376 and EP 759359). Furthermore, a fuel tank is known, which has a multilayered structure and includes an inner layer, an outer layer, and a layer with gasoline barrier properties (i.e., a barrier layer), and in order to enhance the gasoline barrier properties, the barrier layer is arranged closer to the inner layer (see Japanese Laid-Open Patent Publication No.9-29904 and EP 742096).
However, in the manufacture of fuel containers according to these methods, the gasoline permeation amount cannot be suppressed sufficiently. Recently, there are strong demands with respect to the economic consumption of gasoline and the protection of the environment, and there is a strong demand for the reduction of the gasoline permeation amount in fuel containers.